In the art of electrical connectors or electrical interconnection devices for cables and the like, the term cable termination typically means a connector that is or can be used at the end or at an intermediate portion of a cable to connect the conductor or conductors thereof to an external member or members, such as another connector, cable termination, printed circuit board, or the like. Such external member usually is part of or can be connected to at least part of another electrical device, circuit, or the like; in any event, the objective is to effect electrical interconnections of respective circuits, lines, conductors, etc. A cable termination assembly is usually referred to as a combination of a cable termination with an electrical cable. Sometimes the terms cable termination and cable termination assembly equivalently are interchanged, depending on context.
The invention is described in detail below with respect to use of the principles of the invention in a multiconductor cable termination assembly. Such cable termination assembly may be used to connect the conductors of a multiconductor cable, for example, a flat ribbon multiconductor cable (or any other electrical field) to an external member, e.g., as was noted above. The actual cable termination may take the form of a card edge connector.
The discussion below relating to the preferred embodiment of the invention is directed to a multiconductor cable termination assembly. It will be appreciated, nevertheless, that the principles of the invention may be used with a cable having only a single conductor or an assemblage of cables, each having one or more conductors.
Multiconductor electrical cable termination assemblies have been available for a number of years. These cable termination assemblies, in fact, have been available in unassembled form requiring mechanical assembly thereof, which includes the mechanical clamping of the termination properly to secure the various elements of the termination and the cable, and also have been available as a permanent preassembled and molded integral structural combination. Examples of such cable termination assemblies are found in U.S. Pat. No. 3,444,506 and in U.S. Pat. No. 4,030,799, respectively.
In both such patents and the techniques disclosed therein, the junctions or connections of contacts with respective conductors of the cable are made by part of the contacts piercing through the cable insulation to engage a respective conductor. Such a connection is referred to as an insulation displacement connection (IDC).
Unfortunately, contamination of the IDC junctions, e.g., due to dirt, corrosion and the like, can detrimentally affect the junctions, e.g., causing a high impedance, an open circuit or the like. The mechanically assembled types of prior cable terminations are particularly susceptible to such consquences. The directly molded cable termination assemblies are less susceptible to contamination because of a molded hermetic seal or near hermetic seal surrounding the junctions of the cable conductors and contacts. Examples of such directly molded cable termination assemblies are presented in U.S. Pat. No. 4,030,799 and in commonly assigned, U.S. patent application Ser. No. 901,762, filed Aug. 28, 1986, for "Improved Jumper Connector", the disclosures of which are hereby incorporated in their entireties.
Card edge connectors are used to connect the conductors of a cable to terminal pads, conductive traces, etc., that are formed on a printed circuit board or card (printed circuit board and card may be used interchangeably herein). A typical card edge connector includes a plurality of electrical contacts respectively connected to conductors of the cable. The contacts are located in the connector housing in paired opposed positional relation so that when a printed circuit card is inserted into the housing, the respective pairs of contacts engage and electrically connect with respective printed circuit traces or the like on opposite surfaces of the card. Adequate space is provided in the card edge connector housing to permit the card to be inserted a distance sufficient to effect the desired engagement with respective contacts.
One common aspect of both the mechanically assembled cable termination assemblies and the directly molded type is the required assembling step or steps and the separate parts fabrications. These are labor and time consuming and, thus, are relatively expensive. For example, the mechanically assembled devices require the separate molding of several parts followed by assembling thereof. Even in the directly molded device of U.S. Pat. No. 4,030,799, to make a socket connector illustrated therein it is necessary to provide a separately molded cover, to install it over the contacts, and then to secure it, e.g., by ultrasonic welding, to the molded base. It would, of course, be desirable to minimize such mechanical assembly and welding steps and attendant costs. Such elimination of the welding is most desirable because the weld is an area of low strength, and to help assure success of a weld it often is necessary to make the parts of the connector of relatively expensive virgin plastic material.
Conventional card edge connectors may also be manufactured using mechanical assembly techniques as well as techniques that employ the merging of molding and mechanical assembly. These suffer from the same disadvantages mentioned above. Of special consideration when a card edge connector is made using the molding technique of U.S. Pat. No. 4,030,799, for example, is the separating of the opposed pairs of contacts into appropriate positions for installation with respect to the separate cover or housing so that the contacting portions of the contacts ultimately will be positioned in the desired paired opposed relation for resiliently engaging the opposite surfaces of a printed circuit card. A key or spacer has been used in the past temporarily to separate the opposed pairs of contacts while the cover is installed; thereafter, the key or spacer may be removed to permit the respective pairs of contacts resiliently to move toward each other ready for use to engage the opposite surfaces of a printed circuit card inserted into the connector.
Strength and compliance characteristics of the electrical contacts used in a card edge connector require special consideration. In particular, there should be adequate compliance so that the contacts can yield resiliently, for example, as a printed circuit card is inserted into the connector and so that the force exerted by the contacts against the surfaces of the printed circuit card are not so great as to damage the printed circuit traces thereon. This consideration tends to demand a relatively large compliance capability, especially when the actual thickness of printed circuit cards with which the card edge connector is used ordinarily is not closely controlled. The compliance capability of a contact is, in a sense, the ability of the contact to be deformed resiliently to accommodate the insertion of an external member to engagement therewith and the subsequent re-assumption of the original shape, e.g., the undeformed one, when the external member is removed from engaement with the contact. Consistent with such characteristics of compliance, another characteristic is the ability of the contact to undergo such deformation over a relatively wide range without substantial change in the original structure and various force, spring constant, and like characteristics.
Often contrasting with compliance considerations, it is desirable that the contacts be relatively strong to tolerate rough handling, insertion of an incorrectly aligned printed circuit board into the connector, etc. However, the increasing of contact strength often results in the reducing of compliance or, in any event, the increasing of the force with which the contact will press against the surface of a printed circuit card, which, as was mentioned above, should not be so excessive as to damage the traces on the printed circuit card.
One type of female contact, the fork contact, is disclosed in U.S. Pat. No. 4,030,799. A molding method disclosed in such patent is that which sometimes is referred to as insert molding. For such insert molding method, electrical contacts are placed in a mold, a multiconductor cable is placed relative to the contacts and mold, the mold is closed to effect IDC connections of the cable conductors and contacts and to close the mold cavity, and the molding material then is injected into the mold. The fork contacts mentioned are generally planar contacts in that the major extent thereof is in two directions or dimensions (height and width), and the thickness is relatively small; this characteristic makes the fork contacts particularly useful for insert molding.